Spectral module and method for manufacturing spectral module

ABSTRACT

The present invention provides a highly reliable spectral module. When light L 1  proceeding to a spectroscopic unit ( 4 ) passes through a light transmitting hole ( 50 ) in the spectral module ( 1 ) in accordance with the present invention, only the light having passed through a light entrance side unit ( 51 ) formed such as to become narrower toward a substrate ( 2 ) and entered a light exit side unit ( 52 ) formed such as to oppose a bottom face ( 51   b ) of the light entrance side unit ( 51 ) is emitted from a light exit opening ( 52   a ). Therefore, stray light M incident on a side face ( 51   c ) or bottom face ( 51   b ) of the light entrance side unit ( 51 ) is reflected to the side opposite to the light exit side unit ( 52 ) and thus is inhibited from entering the light exit side unit ( 52 ). Therefore, the reliability of the spectral module ( 1 ) can be improved.

TECHNICAL FIELD

The present invention relates to a spectral module for spectrallyresolving and detecting light and a method for manufacturing the same.

BACKGROUND ART

As conventional spectral modules, those described in Patent Literatures1 to 3 have been known, for example. Patent Literature 1 discloses aspectral module comprising a support which transmits light therethrough,an entrance slit for letting the light enter the support, a concavediffraction grating which spectrally resolves and reflects the lighthaving entered the support, and a diode for detecting the lightspectrally resolved and reflected by the concave diffraction grating.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Application Laid-Open No.    4-294223-   Patent Literature 2: Japanese Patent Application Laid-Open No.    2000-65642-   Patent Literature 3: Japanese Patent Application Laid-Open No.    2004-354176

SUMMARY OF INVENTION Technical Problem

In the spectral module disclosed in Patent Literature 1, however, thelight having entered from the entrance slit may become stray lightscattering within the support, thereby lowering the reliability of thespectral module.

In view of such circumstances, it is an object of the present inventionto provide a highly reliable spectral module and a method formanufacturing the spectral module.

Solution to Problem

For achieving the above-mentioned object, the spectral module inaccordance with the present invention comprises a main unit fortransmitting light therethrough; a spectroscopic unit for spectrallyresolving light having entered the main unit from a predeterminedsurface side of the main unit and reflecting the light toward thepredetermined surface; and a photodetector, arranged on thepredetermined surface, for detecting the light spectrally resolved bythe spectroscopic unit; wherein the photodetector has a substrate unitformed with a light transmitting hole for transmitting therethroughlight proceeding to the spectroscopic unit; wherein the lighttransmitting hole includes a light entrance side unit defining a lightentrance opening and a light exit side unit defining a light exitopening; wherein the light entrance side unit is formed such as to havea bottom face substantially parallel to the predetermined surface andbecome narrower toward the predetermined surface; and wherein the lightexit side unit is formed such as to have a side face substantiallyperpendicular to the predetermined surface and oppose the bottom face.

When the light proceeding to the spectroscopic unit passes through thelight transmitting hole in this spectral module, only the light havingentered the light exit side unit formed such as to oppose the bottomface of the light entrance side unit becoming narrower toward thepredetermined surface of the main unit is emitted from the light exitopening. Here, the light incident on the side face or bottom face of thelight entrance side unit is reflected to the opposite side of the lightexit side unit, whereby stray light can be inhibited from entering thelight exit side unit. This can improve the reliability of the spectralmodule.

Preferably, in the spectral module in accordance with the presentinvention, a light absorbing layer for absorbing light is formed betweenthe photodetector and the predetermined surface, the light absorbinglayer has a light transmitting slit for transmitting therethrough lightproceeding to the spectroscopic unit through the light transmittinghole, and the light transmitting slit has a width smaller than theminimal width of the light exit side unit in a direction substantiallyorthogonal to an extending direction of a grating groove formed in thespectroscopic unit.

The resolution of the spectral module is greatly influenced by theminimal width of the slit in a direction substantially orthogonal to theextending direction of the grating groove. Therefore, making the widthof the light transmitting slit smaller than the minimum width of thelight transmitting hole in a direction substantially orthogonal to theextending direction of the grating groove can improve the resolution ofthe spectral module. This is advantageous in improving the reliabilityof the spectral module.

Preferably, in the spectral module in accordance with the presentinvention, the substrate unit is made of a crystalline material, while aside face of the light entrance side unit is formed along a (111)crystal plane. Forming the substrate unit made of a crystalline materialsuch as Si with a side face along the (111) crystal plane of thematerial by wet etching or the like can accurately produce the lightentrance side unit, which makes it possible to form the lighttransmitting hole with high precision, thereby improving the reliabilityof the spectral module.

The method for manufacturing a spectral module in accordance with thepresent invention is a method for manufacturing a spectral modulecomprising a main unit for transmitting light therethrough, aspectroscopic unit for spectrally resolving light having entered themain unit from a predetermined surface side of the main unit andreflecting the light toward the predetermined surface, and aphotodetector for detecting the light spectrally resolved by thespectroscopic unit; the method comprising a photodetector preparationstep of preparing the photodetector having a substrate unit formed witha light transmitting hole; and an arrangement step of arranging thephotodetector prepared in the photodetector and the spectroscopic unitonto the main unit; wherein the photodetector preparation step includesa light entrance side unit formation step of carrying out wet etchingfrom one main face side of the substrate unit so as to form a lightentrance side unit for defining a light entrance opening of the lighttransmitting hole such that the light entrance side unit has a bottomface substantially parallel to the one main face and becomes narrowertoward the other main face, and a light exit side unit formation step ofcarrying out dry etching from the other main face side of the substrateunit after the light entrance side unit formation step so as to form alight exit side unit for defining a light exit opening of the lighttransmitting hole such that the light exit side unit has a side facesubstantially perpendicular to the one main face and opposes the bottomface.

When forming the substrate unit with the light transmitting hole, themethod for manufacturing a spectral module in accordance with thepresent invention carries out wet etching from one main face side of thesubstrate unit, so as to form a light entrance side unit for defining alight entrance opening, and then dry etching from the other main faceside of the substrate unit, so as to form a light exit side unit fordefining a light exit opening. Thus forming the light entrance side unitby wet etching can reduce the time and cost of the photodetectorpreparation step. Accurately forming the light exit side unit by dryetching can produce the light transmitting hole having a stable lighttransmitting characteristic, thereby improving the reliability of thespectral module.

Advantageous Effects of Invention

The present invention can provide a highly reliable spectral module.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of the spectral module in accordance with anembodiment of the present invention;

FIG. 2 is a sectional view taken along the line II-II illustrated inFIG. 1;

FIG. 3 is a bottom face view of the spectral module;

FIG. 4 is an enlarged sectional view of a main part illustrating a lighttransmitting hole;

FIG. 5 is an enlarged plan view of a main part illustrating the lighttransmitting hole;

FIG. 6 is a sectional view for explaining a step of forming a lightentrance side unit;

FIG. 7 is a sectional view for explaining a step of forming a light exitside unit;

FIG. 8 is an enlarged plan view of a main part illustrating a modifiedexample of the light transmitting hole and corresponding to FIG. 5;

FIG. 9 is an enlarged plan view of a main part illustrating a modifiedexample of the light transmitting hole and corresponding to FIG. 5;

FIG. 10 is an enlarged plan view of a main part illustrating a modifiedexample of the light transmitting hole and corresponding to FIG. 5;

FIG. 11 is a sectional view illustrating the spectral module inaccordance with a second embodiment and corresponding to FIG. 2; and

FIG. 12 is a sectional view illustrating the light transmitting hole inaccordance with the second embodiment and corresponding to FIG. 3.

DESCRIPTION OF EMBODIMENTS

In the following, preferred embodiments of the present invention will beexplained in detail with reference to the drawings. In the drawings, thesame or equivalent parts will be referred to with the same signs whileomitting their overlapping descriptions.

First Embodiment

As illustrated in FIGS. 1 and 2, a spectral module 1 comprises asubstrate (main unit) 2 which transmits therethrough light L1 enteringfrom a front face (predetermined surface) 2 a, a lens unit (main unit) 3which transmits therethrough the light L1 entering from an entrancesurface 3 a after passing through the substrate 2, a spectroscopic unit4 for spectrally resolving and reflecting the light L1 having enteredthe lens unit 3, and a photodetector 5 for detecting light L2 spectrallyresolved by the spectroscopic unit 4. The spectral module 1 is a microspectral module which spectrally resolves the light L1 with thespectroscopic unit 4 into the light L2 corresponding to a plurality ofwavelengths and detects the light L2 with the photodetector 5, therebymeasuring a wavelength distribution of the light L1 and the intensity ofa specific wavelength component.

The substrate 2 is formed into a rectangular plate (e.g., having a fulllength of 15 to 20 mm, a full width of 11 to 12 mm, and a thickness of 1to 3 mm) from any of light transmitting glass materials such as BK7,Pyrex (registered trademark), and silica, plastics, and the like. Thefront face 2 a of the substrate 2 is formed with wiring 11 made of amonolayer film of Al, Au, or the like or a multilayer film of Cr—Pt—Au,Ti—Pt—Au, Ti—Ni—Au, Cr—Au, or the like. The wiring 11 has a plurality ofpad units 11 a arranged at a center portion of the substrate 2, aplurality of pad units 11 b arranged at one longitudinal end portion ofthe substrate 2, and a plurality of connection units 11 c for connectingthe corresponding pad units 11 a, 11 b to each other. On the front face2 a side of the substrate 2, the wiring 11 has an antireflection layermade of a monolayer film of CrO or the like or a multilayer film ofCr—CrO or the like.

A light absorbing layer 13 formed on the front face 2 a of the substrate2 has a slit (light transmitting slit) 13 a which transmits therethroughthe light L1 proceeding to the spectroscopic unit 4 through a lighttransmitting hole 50 (which will be explained later) of thephotodetector 5 and an opening 13 b through which the light L2proceeding to a light detection unit 5 b (which will be explained later)of the photodetector 5 passes. Examples of materials for the lightabsorbing layer 13 include black resists, color resins (e.g., silicone,epoxy, acrylic, urethane, polyimide, and composite resins) containingfillers (e.g., carbon and oxides), metals and metal oxides of Cr, Co,and the like, their multilayer films, and porous ceramics and metals andmetal oxides.

As illustrated in FIGS. 2 and 3, the lens unit 3 is formed from the samematerial as that of the substrate 2, a light transmitting resin, a lighttransmitting inorganic/organic hybrid material, a light transmittinglow-melting glass material for forming a replica, a plastic, or the likeinto such a form that a semispherical lens is cut off by two planessubstantially parallel to each other and substantially orthogonal to itsentrance surface (bottom face) 3 a so as to form side faces 3 b (e.g.,with a radius of curvature of 6 to 10 mm, a height of 5 to 8 mm, and theentrance surface 3 a having a full length of 12 to 18 mm and a fullwidth (distance between the side faces 3 b) of 6 to 10 mm, and functionsas a lens focusing the light L2 spectrally resolved by the spectroscopicunit 4 onto the light detection unit 5 b of the photodetector 5. Thelens form may be either spherical or aspherical.

The spectroscopic unit 4 is a reflection-type grating having adiffraction layer 6 formed on the outer surface of the lens unit 3, areflecting layer 7 formed on the outer surface of the diffraction layer6, and a passivation layer 8 covering the diffraction layer 6 andreflecting layer 7. The diffraction layer 6 is formed by arranging aplurality of grating grooves 6 a in a row along the longitudinaldirection of the substrate 2, while the extending direction of thegrating groves 6 a substantially coincides with a directionsubstantially orthogonal to the longitudinal direction of the substrate2. The diffraction layer 6, which employs sawtooth blazed gratings,rectangular binary gratings, or sinusoidal holographic gratings, forexample, is formed by photocuring an optical resin for a replica such asa photocurable epoxy, acrylic, or organic/inorganic hybrid resin. Thereflecting layer 7, which is shaped like a film, is formed byvapor-depositing Al, Au, or the like onto the outer surface of thediffraction layer 6, for example. Regulating the area by which thereflecting layer 7 is formed can adjust the optical NA of the spectralmodule 1. The lens unit 3 and the diffraction layer 6 constituting thespectroscopic unit 4 can be formed integrally by the materials mentionedabove. The passivation layer 8, which is shaped like a film, is formedby vapor-depositing MgF₂, SiO₂, or the like onto the outer surfaces ofthe diffraction layer 6 and reflecting layer 7, for example.

As illustrated in FIGS. 1, 2, and 4, the photodetector 5 has arectangular semiconductor substrate 5 a (substrate unit) (e.g., with afull length of 5 to 10 mm, a full width of 1.5 to 3 mm, and a thicknessof 0.1 to 0.8 mm) arranged on the front face 2 a of the substrate 2. Thesemiconductor substrate 5 a is made of a crystalline material such asSi, GaAs, InGaAs, Ge, or SiGe.

The light detection unit 5 b is formed on the surface of thesemiconductor substrate 5 a on the spectroscopic unit 4 side. The lightdetection unit 5 b is a CCD image sensor, a PD array, a CMOS imagesensor, or the like, in which a plurality of channels are arranged in arow along a direction substantially orthogonal to the extendingdirection of the grating grooves 6 a in the spectroscopic unit 4 (i.e.,along the arranging direction of the grating grooves 6 a). A lightshielding layer 12 constituted by Al, Au, or the like is formed by vapordeposition on the surface of the semiconductor substrate 5 a opposite tothe spectroscopic unit 4.

When the light detection unit 5 b is a CCD image sensor, the intensityinformation of light at its incident position on two-dimensionallyarranged pixels is subjected to line binning, so as to yield lightintensity information at one-dimensional positions, and the intensityinformation at the one-dimensional positions is read in time series.That is, a line of pixels subjected to line binning forms one channel.In the case where the light detection unit 21 is a PD array or CMOSsensor, intensity information of light at its incident position onone-dimensionally arranged pixels is read in time series, whereby onepixel forms one channel.

When the light detection unit 5 b is a PD array or CMOS image sensor inwhich pixels are arranged two-dimensionally, a line of pixels aligningin a one-dimensional arrangement direction parallel to the extendingdirection of the grating grooves 6 a of the spectroscopic unit 4 formsone channel. When the light detection unit 5 b is a CCD image sensor,one having a channel interval in the arrangement direction of 12.5 μm, achannel full length (length of the one-dimensional pixel row subjectedto line binning) of 1 mm, and 256 arrangement channels, for example, isused for the photodetector 5.

As illustrated in FIGS. 2, 4, and 5, the semiconductor substrate 5 a isformed with a light transmitting hole 50, disposed in parallel with thelight detection unit 5 b in the channel arrangement direction, fortransmitting the light L1 proceeding to the spectroscopic unit 4. Thelight transmitting hole 50, which extends in a direction substantiallyorthogonal to the front face 2 a of the substrate 2, is formed byetching or the like while being aligned with the light detection unit 5b with high precision.

The light transmitting hole 50 is constituted by a light entrance sideunit 51 defining a light entrance opening 51 a through which the lightL1 enters and a light exit side unit 52 defining a light exit opening 52a through which the light L1 exits. The light entrance side unit 51 isformed into a substantially truncated quadrilateral pyramid so as tobecome narrower toward the front face 2 a of the substrate 2 and has abottom face 51 b which is substantially parallel to the front face 2 aof the substrate 2.

The light exit side unit 52, which is formed into a substantiallyquadrangular prism from the surface of the semiconductor substrate 5 aon the spectroscopic unit 4 side so as to oppose the bottom face 51 b ofthe light entrance side unit 51 and connect therewith, has a side face52 b substantially perpendicular to the front face 2 a of the substrate2. The light exit side unit 52 is formed such that its width H1 (minimalwidth) is greater than the width H2 of the slit 13 a of the lightabsorbing layer 13 in the channel arrangement direction of the lightdetection unit 5 b (i.e., in a direction substantially orthogonal to theextending direction of the grating grooves 6 a).

An underfill material 15 which transmits at least the light L2therethrough is provided between the semiconductor substrate 5 a and thesubstrate 2 or light absorbing layer 13. The surface of thesemiconductor substrate 5 a on the substrate 2 side is formed with arectangular ring-shaped projection 53 which surrounds the light exitopening 52 a, whereby the provided underfill material 15 is blocked bythe projection 53 before reaching the light exit opening 52 a. Thisprevents the underfill material 15 from entering the light transmittinghole 50, whereby light can enter the main unit 2 without being refractedor dispersed by the underfill material 15. External terminals of thephotodetector 5 are electrically connected by wire-bonding through bumps14 to the pad units 11 a exposed from the light absorbing layer 13. Thepad units 11 b are electrically connected to external electric devices(not depicted).

A method for manufacturing the above-mentioned spectral module 1 willnow be explained.

First, the photodetector 5 is prepared. For example, the semiconductorsubstrate 5 a constituted by Si is subjected to alkali etching using KOH(potassium hydroxide), TMAH (tetramethylammonium hydroxide), or thelike, so as to form the rectangular ring-shaped projection 53surrounding the scheduled light exit opening 52 a. Thereafter, the lightdetection unit 5 b, wiring, and electrode pads are prepared on the othermain face B side.

Subsequently, a mask is opened at a predetermined position byphotolithography using double-sided alignment with reference to thelight detection unit 5 b, and alkali etching is carried out, so as toform the light entrance side unit 51 shaped into a substantiallytruncated quadrilateral pyramid (see FIG. 6). Here, by alkali etching,the semiconductor substrate 5 a constituted by Si, for example, isformed with a side face 51 c of the light entrance side unit 51 along a(111) crystal plane which is tilted by about 55° with respect to a (100)crystal plane. Then, by photolithography with reference to the lightdetection unit 5 b, the other main face B of the semiconductor substrate5 a is subjected to silicon deep dry etching using plasma discharge at apredetermined position, so as to form the light exit side unit 52 shapedinto a substantially quadrangular prism opposing the bottom face 51 b ofthe light entrance side unit 51 (see FIG. 7). Thus, the lighttransmitting hole 50 extending in a direction substantially orthogonalto one main face A of the semiconductor substrate 5 a is formed.Thereafter, the light shielding layer 12 is formed by vapor-depositingAl, Au, or the like onto one main face A and the side face 51 c andbottom face 51 b of the light entrance side unit 51, and the wafer isdiced with reference to the light detection unit 5 b, so as to preparethe photodetector 5.

Next, the lens unit 3 is formed with the spectroscopic unit 4.Specifically, a light transmitting master grating inscribed withgratings corresponding to the diffraction layer 6 is pressed against anoptical resin for a replica dripped near the vertex of the lens unit 3.The optical resin for a replica is cured by irradiation with light inthis state, and then preferably cured by heating for stabilization, soas to form the diffraction layer 6 having a plurality of grating grooves6 a. Thereafter, the master grating is released, Al, Au, or the like isvapor-deposited onto the outer surface of the diffraction layer 6 whollyor through a mask, so as to form the reflecting layer 7, and MgF₂, SiO₂,or the like is further vapor-deposited onto the outer surfaces of thediffraction layer 6 and reflecting layer 7, so as to form thepassivation layer 8.

On the other hand, the substrate 2 is prepared, and the light absorbinglayer 13 having the slit 13 a and opening 13 b is formed on the frontface 2 a of the substrate 2. Here, the slit 13 a and opening 13 b areformed such as to have a predetermined positional relationship withrespect to an outer edge portion of the substrate 2 serving as areference for positioning the spectroscopic unit 4 on the substrate 2.

The photodetector 5 is mounted on the light absorbing layer 13 byface-down bonding. Subsequently, the underfill material 15 is providedbetween the photodetector 5 and the front face 2 a of the substrate 2.Thereafter, with reference to the outer edge portion of the substrate 2,the lens unit 3 formed with the spectroscopic unit 4 is bonded to therear face 2 b of the substrate 2 with an optical resin agent 18, so asto yield the spectral module 1. Here, the photodetector 5 and thesubstrate 2 are electrically connected to each other through the bumps14.

Operations and effects of the above-mentioned spectral module 1 will nowbe explained.

When the light L1 proceeding to the spectroscopic unit 4 passes throughthe light transmitting hole 50 in the spectral module 1, only the lighthaving entered the light exit side unit 52 formed such as to oppose thebottom face 51 b of the light entrance side unit 51 becoming narrowertoward the substrate 2 is emitted from the light exit opening 52 a.Here, stray light M incident on the bottom face 51 b or side face 51 cof the light entrance side unit 51 is reflected toward the lightentrance opening 51 a, and thus is inhibited from entering the lightexit side unit 52. This can improve the reliability of the spectralmodule 1.

In this spectral module 1, subjecting the semiconductor substrate 5 a ina wafer state to alkali etching can collectively form the light entranceside unit 51, thereby reducing the time and cost in the step ofpreparing the photodetector 5.

Carrying out silicon deep dry etching from the other main face B of thesemiconductor substrate 5 a can accurately form the light exit side unit52, so as to produce the light transmitting hole 50 having a stablelight transmitting characteristic, thereby improving the reliability ofthe spectral module 1. Specifically, since the light exit side unit 52is formed from the other main face B side where the light detection unit5 b is arranged, the positional accuracy of the light exit side unit 52with respect to the light detection unit 5 b on the same plane can beraised in the spectral module 1. Since the light passing through thelight exit side unit 52 of the light transmitting hole 50 is diffractedand reflected by the grating grooves 6 a of the spectroscopic unit 4 anddetected by the light detection unit 5 b, the reliability of thespectral module 1 can be improved when the positional accuracy betweenthe light exit side unit 52 and the light detection unit 5 b is raised.Further, the form of the opening cross section of the light exit sideunit 52 (i.e., the form of the light exit opening 52 a) is opticallyfocused at the light detection unit 5 b, while the channel of the lightdetection unit 5 b is arranged so as to correspond to the minimal widthof the light exit side unit 52 in the longitudinal direction of thesemiconductor substrate 5 a. Therefore, the resolution of the spectralmodule 1 is greatly influenced by the minimal width of the light exitside unit 52 in the channel arrangement direction. Hence, accuratelyforming the light exit side unit 52 by silicon deep dry etching caninhibit the resolution from fluctuating among products and improve thereliability of the spectral module 1.

In this spectral module 1, the semiconductor substrate 5 a isconstituted by a crystalline material such as Si, so that the lightentrance side section 51 can be formed accurately when a side face isformed along a (111) crystal plane of the material by alkali etching,whereby the light transmitting hole 50 can be formed with highprecision. Therefore, the reliability of the spectral module 1 can beimproved.

In a direction substantially orthogonal to the extending direction ofthe grating grooves 6 a, the resolution of the spectral module 1 isgreatly influenced by the minimal width of a slit through which lightpasses. Therefore, making the width H2 of the slit 13 a in the lightabsorbing layer 13 smaller than the minimum width H1 of the lighttransmitting hole 50 in the photodetector 5 in a direction substantiallyorthogonal to the extending direction of the grating grooves 6 a canimprove the resolution of the spectral module 1. This is advantageous inimproving the reliability of the spectral module 1.

As illustrated in FIG. 8, in a light transmitting hole 60 formed in thephotodetector 5, a light exit side unit 62 having a side face 62 bsubstantially perpendicular to a bottom face 61 b of a light entranceside unit 61 may be formed with an oblong cross section. As illustratedin FIG. 9, a light exit side unit 72 may be made longer than that inFIG. 5 in a direction substantially orthogonal to the longitudinaldirection (i.e., in the extending direction of the grating grooves 6 a),so that the width of a bottom face 71 b of a light entrance side unit 71and the width of the opening cross section of the light exit side unit72 equal each other, i.e., the side face 72 b of the light exit sideunit 72 and the side face 71 c of the light entrance side unit 71 aredirectly joined together. As illustrated in FIG. 10, a light exit sideunit 82 may be made further longer than that in FIG. 9, so that thewidth of the opening cross section in the light exit side unit 82 isgreater than the width of a bottom face 81 b of a light entrance sideunit 81 in a direction substantially orthogonal to the longitudinaldirection of the semiconductor substrate 5 a.

Second Embodiment

A spectral module 21 in accordance with the second embodiment differsfrom the spectral module 1 in accordance with the first embodiment inthe structure of the photodetector and in that a wiring board isarranged on the front face of the substrate.

In the spectral module 21, as illustrated in FIGS. 11 and 12, aplurality of terminal electrodes 23 are formed on a surface of thephotodetector 22 on the side opposite to the spectroscopic unit 4. Theterminal electrodes 23 are connected to their corresponding pad units 24of a wiring board 24 with wires 26. This electrically connects theterminal electrodes 23 to the wiring board 24, whereby an electricsignal generated in a light detection unit 22 b is taken out through theterminal electrodes 23 and pad units 24 a and 24 b of the wiring board24.

A light transmitting hole 90 formed in the semiconductor substrate 22 ais constituted by a light entrance side unit 91 defining a lightentrance opening 91 a and a light exit side unit 92 defining a lightexit opening 92 a. The light entrance side unit 91 has a side face 91 bsubstantially perpendicular to the front face 2 a of the substrate 2.The light exit side unit 92 is formed into a substantially truncatedquadrilateral pyramid so as to become wider toward the front face 2 a ofthe substrate 2 and has an upper face 92 a which is substantiallyparallel to the front face 2 a of the substrate 2. The light entranceside unit 91 is formed into a substantially quadrangular prism opposingthe upper face 92 b of the light exit side unit 92, while its side face91 b is joined to the upper face 92 b of the light exit side unit 92. Alight absorbing layer 27 formed on the front face 2 a of the substrate 2has a slit (light transmitting slit) 27 a which is narrower than theminimal width of the light entrance side unit 91 in a directionsubstantially orthogonal to the extending direction of the gratinggrooves 6 a of the spectroscopic unit 4.

A method for manufacturing the above-mentioned spectral module 21 willnow be explained.

First, the photodetector 22 is prepared. For example, on a semiconductorsubstrate 22 a in a wafer state constituted by Si, the light detectionunit 22, wiring, and electrode pads are prepared on the other main faceB side. Thereafter, Al, Au, or the like is vapor-deposited on aninsulating film such as SiO₂ on the other main face B, so as to form alight shielding layer 29, thereby preparing the photodetector 22.

Subsequently, alkali etching using KOH (potassium hydroxide), TMAH(tetramethylammonium hydroxide), or the like, dry etching, and the likeare carried out, so as to form a rectangular ring-shaped projection 93surrounding the scheduled light exit opening 92 a. Thereafter, on onemain face A of the semiconductor substrate 22 a, a mask is opened at apredetermined position by photolithography using double-sided alignmentwith reference to the light detection unit 22 b, and alkali etchingusing KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide)is carried out, so as to form the light entrance side unit 92 shapedinto a substantially truncated quadrilateral pyramid. Then, the othermain face B of the semiconductor substrate 22 a is subjected to silicondeep dry etching using plasma discharge at a predetermined position, soas to form the light entrance side unit 91 shaped into a substantiallyquadrangular prism joined to the bottom face 92 b of the light exit sideunit 92. Thus, the light transmitting hole 90 extending in a directionsubstantially orthogonal to one main face A of the semiconductorsubstrate 5 a is formed. Thereafter, the light shielding layer 29 isformed by vapor-depositing Al, Au, or the like onto one main face A andthe side face 91 c and bottom face 91 b of the light entrance side unit91, and the wafer is diced with reference to the light detection unit 22b, so as to prepare the photodetector 22.

Subsequently, with reference to outer edge portions of the photodetector22 and substrate 2 or alignment marks, the other main face B side of thephotodetector 22 is bonded to the front face 2 a of the substrate 2 withan optical resin material 17. Thereafter, the terminal electrodes 23 ofthe photodetector 22 are connected to their corresponding pad units 24 aof the substrate 2 with the wires 26. The pad units 24 a areelectrically connected to their corresponding terminal pad units 24 bthrough a wiring layer 19. A light absorbing layer made of a blackresist or the like is arranged at an outer peripheral portion of thephotodetector 22 in the substrate 2 and thus can absorb disturbancelight and reflected light which is unnecessary as a signal from thespectroscopic unit 4, thereby securing the reliability.

The lens unit 3 formed with the spectroscopic unit 4 is bonded to therear face 2 b of the substrate 2 with the optical resin agent 18 withreference to the outer edge portion of the substrate 2, so as to yieldthe spectral module 21.

By collectively forming the light exit side unit 92 by subjecting thesemiconductor substrate 22 a in a wafer state to alkali etching, theabove-mentioned spectral module 21 in accordance with the secondembodiment can reduce the time and cost in the step of preparing thephotodetector 22. Carrying out silicon deep dry etching from the othermain face B of the semiconductor substrate 5 a can accurately form thelight exit side unit 52, so as to produce the light transmitting hole 50having a stable light transmitting characteristic, thereby improving thereliability of the spectral module 1.

The present invention is not limited to the above-mentioned embodiments.

For example, the form of the light entrance side unit in the firstembodiment and the light exit side unit in the second embodiment is notlimited to the substantially truncated quadrilateral pyramid as long asit has a bottom face (upper face) substantially parallel to the frontface 2 a of the substrate 2 and becomes narrower toward the front face 2a of the substrate 2. Similarly, the form of the light exit side unit inthe first embodiment and the light entrance side unit in the secondembodiment is not limited to the substantially quadrangular prism aslong as it has a side face substantially perpendicular to the front face2 a of the substrate 2 and opposes the bottom face (upper face) of thelight entrance side unit (light exit side unit) paired therewith.

The light transmitting hole is not limited to the mode in which thelight entrance side unit and the light exit side unit are directlyjoined together, but may be provided with an intermediate unit (e.g., apart having a different angle of inclination of the side face or adifferent opening cross-sectional form).

The light entrance side unit in the first embodiment and the light exitside unit in the second embodiment may be formed not only by alkalietching, but also by various kinds of wet etching and dry etching.Similarly, the light exit side unit in the first embodiment and thelight entrance side unit in the second embodiment may be formed not onlyby silicon deep dry etching but also by various kinds of dry etching.

The above-mentioned first embodiment may employ the structure of thelight transmitting hole in the second embodiment, while the secondembodiment may employ the structure of the light transmitting hole inthe first embodiment.

INDUSTRIAL APPLICABILITY

The present invention can provide a highly reliable spectral module.

REFERENCE SIGNS LIST

1, 21 . . . spectral module; 2 . . . substrate (main unit); 2 a . . .front face (predetermined surface); 3 . . . lens unit (main unit); 4 . .. spectroscopic unit; 5, 22 . . . photodetector; 5 a, 22 a . . .semiconductor substrate; 5 b, 22 b . . . light detection unit; 6 . . .diffraction layer; 6 a . . . grating groove; 13, 27 . . . lightabsorbing layer; 50, 60, 70, 80, 90 . . . light transmitting hole; 51,61, 71, 81, 91 . . . light entrance side unit; 52, 62, 72, 82, 92 . . .light exit side unit; 51 a, 61 a, 71 a, 81 a, 91 a . . . light entranceopening; 51 b, 61 b, 71 b, 81 b . . . bottom face; 51 c, 61 c, 71 c, 81c, 92 c . . . side face; 52 a, 62 a, 72 a, 82 a, 92 a . . . light exitopening; 92 b . . . upper face (bottom face); 52 b, 62 b, 72 b, 82 b, 91b . . . side face; A . . . one main face; B . . . the other main face

The invention claimed is:
 1. A spectral module comprising: a main unitfor transmitting light therethrough; a spectroscopic unit for spectrallyresolving light having entered the main unit from a predeterminedsurface side of the main unit and reflecting the light toward thepredetermined surface; and a photodetector, arranged on thepredetermined surface, for detecting the light spectrally resolved bythe spectroscopic unit; wherein the photodetector has a substrate unitformed with a light transmitting hole for transmitting therethroughlight proceeding to the spectroscopic unit; wherein the lighttransmitting hole includes a light entrance side unit defining a lightentrance opening and a light exit side unit defining a light exitopening; wherein the light entrance side unit is formed such as to havea bottom face substantially parallel to the predetermined surface andbecome narrower toward the predetermined surface; and wherein the lightexit side unit is formed such as to have a side face substantiallyperpendicular to the predetermined surface and oppose the bottom face.2. A spectral module according to claim 1, wherein a light absorbinglayer for absorbing light is formed between the photodetector and thepredetermined surface; wherein the light absorbing layer has a lighttransmitting slit for transmitting therethrough light proceeding to thespectroscopic unit through the light transmitting hole; and wherein thelight transmitting slit has a width smaller than the minimal width ofthe light exit side unit in a direction substantially orthogonal to anextending direction of a grating groove formed in the spectroscopicunit.
 3. A spectral module according to claim 1, wherein the substrateunit is made of a crystalline material; and wherein a side face of thelight entrance side unit is formed along a (111) crystal plane.
 4. Amethod for manufacturing a spectral module comprising a main unit fortransmitting light therethrough, a spectroscopic unit for spectrallyresolving light having entered the main unit from a predeterminedsurface side of the main unit and reflecting the light toward thepredetermined surface, and a photodetector for detecting the lightspectrally resolved by the spectroscopic unit, the method comprising: aphotodetector preparation step of preparing the photodetector having asubstrate unit formed with a light transmitting hole; and an arrangementstep of arranging the photodetector prepared in the photodetector andthe spectroscopic unit onto the main unit; wherein the photodetectorpreparation step includes: a light entrance side unit formation step ofcarrying out wet etching from one main face side of the substrate unitso as to form a light entrance side unit for defining a light entranceopening of the light transmitting hole such that the light entrance sideunit has a bottom face substantially parallel to the one main face andbecomes narrower toward the other main face; and a light exit side unitformation step of carrying out dry etching from the other main face sideof the substrate unit after the light entrance side unit formation stepso as to form a light exit side unit for defining a light exit openingof the light transmitting hole such that the light exit side unit has aside face substantially perpendicular to the one main face and opposesthe bottom face.